1. Field of the Invention
The invention is directed to a cylinder for a hydraulic system having a housing in which a seal is held in a predetermined position, the seal being produced from an elastic material and having a sealing lip for contacting a piston that is axially movably arranged in the cylinder and a sealing bead pretensioned against the housing and deformable under this pretensioning.
2. Description of the Related Art
A seal for insertion in a cylinder housing for contacting a piston movably arranged in the cylinder housing is disclosed, for example, by German reference DE A 197 14 844 A1. The seal has two sealing beads which are arranged at a distance from one another and project outward radially. These sealing beads are very narrow in relation to the width of the seal. The seal also has a sealing lip for contacting the piston. An edge of the sealing lip contacts the piston and slides during a longitudinal movement of the piston along the cylinder. This type of seal seals a pressure space of the cylinder relative to a pressure difference. In the pressureless state of the cylinder, the sealing of the pressure space is produced exclusively by the elastic pretensioning of the sealing bead and sealing lip. When there is high pressure in the pressure space, the sealing lip and the sealing bead are pressed with particularly high forces against the piston and the housing.
A problem in the known cylinder is that the sealing bead moves in the axial direction relative to the housing during pressure fluctuations in the pressure space and during oscillating movement of the piston because the seal deforms under pressure. The axial movement wears the area of the seal contacting the housing.
The object of the present invention is to design a cylinder having a housing and a seal with a sealing lip for contacting a piston axially movably mounted in the cylinder, so that a pressure space defined by the cylinder is sealed in a particularly reliable manner and exhibits particularly low wear of the seal.
According to an embodiment of the present invention, a cylinder having a housing for receiving a piston has a supporting part in the cylinder which is independent from the piston and is associated with the sealing bead for generating a supporting force required for pretensioning the sealing bead against the housing of the cylinder.
As a result of this design, the sealing bead may be pretensioned against the housing with a particularly high force given a suitable design of the supporting part. This arrangement of the supporting part avoids supporting of the sealing bead at the piston, as is done in the above-mentioned prior art. Accordingly, the inventive arrangement ensures that the sealing bead on the housing is not additionally deformed by pressure fluctuations in the pressure space. Since the seal is not deformed or axially moved by pressure fluctuations, the seal has particularly low wear and the pressure space is dependably sealed. Furthermore, volume losses and path losses are prevented in the hydraulic system through reliable holding of the seal on the housing. Particularly when the cylinder is used as a slave cylinder in the hydraulic system, the movements of the piston and pressure fluctuations in the pressure space do not result in significant wear of the seal.
According to a further embodiment of the invention, the construction of the supporting part may comprise a simple annular element formed to enclose the piston concentrically in a sleeve-shaped manner.
The annular element includes a high stability and is therefore capable of receiving especially high forces when it comprises a radial extending web along the circumference. Further, the radial extending web may be used to secure the seal in the axial direction.
In the known cylinder, the seal is inserted in a recess of the housing. The recess is defined in the axial direction by a guide sleeve. However, since the seal of the known cylinder has radial and axial play in the recess, the seal moves in the pressure space during pressure fluctuations. According to another embodiment of the present invention, movements of the seal relative to the guide sleeve are prevented in a particularly dependable manner when the supporting part is constructed in one piece with a guide sleeve which is detachably connected with the housing.
The mounting of the cylinder according to the invention is particularly simple in an embodiment of the present invention when the supporting part is arranged inside the seal.
According to another embodiment of the invention, relative movements of the seal due to especially high pressures in the pressure space are prevented in a simple structure when the supporting part directly contacts a surface of the housing or guide sleeve located opposite to the pressure space.
The sealing bead of the seal may comprise a narrow edge. However, the sealing bead may reliably hold the seal in its intended position also in case of extensive pressure fluctuations when the sealing bead is slightly wider than a distance between the supporting part and the housing.
The sealing bead may, for example, be clamped in between the guide sleeve and a sealing surface arranged perpendicular to the direction of movement of the piston. For this purpose, however, the cylinder requires an elaborate axial pretensioning of the guide sleeve. The cylinder according to the invention is constructed in a particularly simple manner when the sealing bead projects in a pipe-shaped manner from the seal and is arranged concentric to the piston.
According to another embodiment of the present invention, high pressure in the pressure space is prevented from escaping between the sealing bead and the housing when the sealing bead projecting in a pipe-shaped manner from the seal is arranged on the side of the seal located opposite to a pressure space of the cylinder. Due to this design, the seal is pushed toward the sealing bead by the pressure of the sealing space, so that the sealing bead is pressed between the housing and the supporting part.
According to another embodiment of the present invention, the seal is held in its intended position in a particularly reliable manner when a first structural component part of the cylinder has a depression for receiving a partial area of the sealing bead. The sealing bead is accordingly connected with the depressions in a positive engagement, so that movements of the remaining portion of the seal do not cause friction between the sealing bead and the housing.
Furthermore, the depression formed in a first structural component part may be formed as a circumferentially extending groove to contribute to increased tightness. The first structural component part includes at least one of the supporting part and the housing.
To facilitate the mounting of the cylinder according to the invention, the sealing bead may comprise a contour corresponding to the depression. Accordingly, the seal may be pre-mounted at the first structural component part having the depression. The seal is held at this first structural component part by the contour of the sealing bead so that a second structural component part may be mounted while the seal is held in place on the first structural component part. The depressions in the first structural component part and the contour of the sealing bead therefore act as retaining means while the cylinder according to the invention is being mounted.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.